This invention relates to stepping motor controls and specifically to a stepping motor driver circuit.
Stepping motors are intended for use in applications requiring precise control of displacement. This is achieved by incremental radial displacement of the motor shaft under the control of a DC supply voltage sequentially applied to the multiple windings of the motor.
To attain relatively high overall rotational velocities, it is generally necessary to apply at the outset of winding excitation a supply voltage which is higher than the normal operating voltage in order to rapidly produce sufficient initial torque-producing current. In many known prior art motor drivers, multiple voltage power supplies have been employed to provide the desired excitation.
Motor windings, being inductive in nature, resist changes in current magnitude and direction. The presence of a residual current in a motor winding after excitation must be quickly dissipated to avoid improper operation of the motor. In many prior art driver circuits, relatively high wattage damping resistors are employed to reduce winding currents and to remove excess current during the periods when the motor windings are not excited. As a result, a substantial amount of power is wasted in the dropping resistors. Therefore, the power supply or supplies of prior art stepping motor drivers, needed a current capacity capable of providing both the useful power and the dissipated power in order to excite the stepping motor according to the desired torque characteristic.